Sorting apparatus



Nov. 9, 1965 L. KELLY ETAL SORTING APPARATUS 3 Sheets-Sheet 1 Filed Aug. 25, 1964 I NTOR B W iffim PATENT AGENT Nov. 9, 1965 KELLY ETAL SORTING APPARATUS 3 Sheets-Sheet 2 Filed Aug. 26, 1964 HAY @W QM PATENT AGENT Nov. 9, 1965 L. KELLY ETAL SORTING APPARATUS 3 Sheets-Sheet 3 Filed Aug. 26, 1964 NV T R PATENT AGENT United States Patent 3,216,567 SORTING APPARATUS Leonard Kelly and James Francis Hutter, Bancroft, Ontario, Canada, assignors, by mesne assignments, to Sphere Investments Limited, Nassau, Bahama Islands, a corporation of the Bahama Islands Filed Aug. 26, 1964, Ser. No. 392,118 16 Claims. (Cl. 209-81) This application is a continuati-on-in-part of United States patent application Serial No. 319,244 filed October 28, 1963, now abandoned.

This invention relates to apparatus for sorting moving bodies of material, and in particular it relates to apparatus for sorting moving bodies of material according to their electrical characteristics.

Relatively large groups of materials possess the property of electrical resistance in amounts which are measurable in practice. Frequently the resistance of the material is related to the amount of a desired constituent in the body. Consequently, electrical resistance, or its reciprocal conductance, provides a desirable basis on which to sort.

One example of a material having an individual resistance characteristic related to the amount of a constituent dispersed therein is a rock material. It has long been known that different rock materials have different values of resistances associated with them, and because of increasing labour costs in recent years the mechanical sorting of rock fragments appears to be more and more desirable. The present invention is therefore particularly useful in the ore sorting field and will be discussed mainly in this connection in the subsequent description. However, it is not the intention to limit the invention to the sorting of rock or ore fragments. Where the invention is described for convenience in connection with the sorting of rock fragments, it is intended that it may be applied to any bodies of material composed of constituents having differing electrical characteristics.

In the past, attempts have been made to utilize the property of electrical resistance for mechanical sorting. The prior art apparatus generally was complex and was not able to operate with suificient speed to make the sorting economically feasible. In the case of the sorting of rock fragments, it apparently was not recognized that the resistance of the ore and the resistance of the waste in any particular ore body was relatively consistent and that the ore and waste resistances are frequently of quite different values.

One particular type of prior art apparatus makes an actual resistance measurement of the resistance of each body as it moves through the apparatus, and compares the measured resistance to a predetermined value. The subsequent sorting is based on the comparison. The measuring and comparing equipment is complex and often tends to be disturbed by external conditions.

The present invention seeks to overcome disadvantages in prior art sorting apparatus. Briefly, the present invention in one form is for an apparatus for sorting bodies of material moving through a sorting zone. In the sorting zone there is at least a pair of high voltage electrodes having terminating ends in juxtaposition with a predetermined path followed by the bodies through the zone. The electrodes are spaced apart to prevent open pathway current flow between them, that is to prevent current flow between them in the absence of material to be sorted. A current flow detection means is con- Patented Nov. 9, 1965 "ice nected to the electrodes and is responsive to an ionizing discharge current flow for developing a signal with movement of discharge initiating body along the predetermined path past the electrodes. Rejection means positioned in the sorting zone so that bodies of material pass it after passing the electrodes, has a first condition where bodies are moved or directed to a first path, and a second condition where bodies are moved or directed to a second path. The rejection means is controlled in response to the signal from the detection means. That is, the rejection means may be actuated to one condition or the other by either the presence or absence of a signal from the detection means as will be explained hereinafter.

Thus, the bodies of material are directed along the predetermined path through the sorting zone past the electrodes. A high voltage is applied to the electrodes and the level of the high voltage is such that there is no discharge between the electrodes in the absence of a body of material therebetween or when a body of material has constitutents providing electrical characteristics inhibiting ionizing discharge current flow, but there is an ionizing discharge initiated between electrodes through a body of material or over its surface when the body has constituents providing electrical characteristics permitting such discharge flow. By appropriate selection of the high voltage level or by using a selected predetermined level of ionizing current flow to which the rejection means is responsive, it is possible to differentiate between bodies of material which have different amounts of a desirable constitutent or constitutents, or which have different compositions and hence which have different electrical characteristics. That is, when a body contains sufficient conductive constitutent, there may be initiated an ionizing discharge between the electrodes and the body surface or there may be at least a partial contact discharge if the electrodes actually contact the body surface, and, in conjunction, there will be a current flow through the body itself or over its surface that may be referred to as a type of ionizing discharge where the discharge occurs between relatively conductive particles or portions of the body. If the body of material has an insuflicient amount of conductive constitutent, no ionizing discharge current flow takes place. It is the degree of this ionizing discharge current flow which is used to actuate the rejection means.

It should be noted that the current flow on which the sorting is based is an ionizing or spark discharge type of current flow. This type of current flow results when using a voltage high enough to produce at least partial breakdown or ionization of some portion of the body of material subjected to the voltage or of some of the surrounding gases. Thus, the term high voltage as used herein is intended to mean a voltage sufficiently high to cause in certain of the material being examined an ionizing discharge current flow as distinguished from ordinary linear current flow. This linear type of current flow is used, for example, in a prior apparatus which determines the resistance of each body from a normal or linear current flow. In this prior apparatus, there is a normal current flow to some degree through each body, although the current flow is small and in the case of high resistance bodies is extremely small. In this prior apparatus, the current flow is compared within the apparatus to a predetermined standard. In the case of high resistance bodies, sensitive equipment is required. In the present invention, the ionizing discharge type of flow is of a comparatively high value permitting the use of more rugged current detection means.

It should be noted that a body of material may have one value of resistance when measured by the usual low voltage method and a different value when calculated from voltage and current readings obtained from the apparatus of this invention used as subsequently described. There is normally a linear relationship between voltage and current associated with a particular body when obtained with the customary low voltage methods. However, the relationship between voltage and current readings may not be linear when obtained from the apparatus of this invention when used as subsequently described. The readings may, of course, include various factors outside the body itself, such as, for example, resistance of air' between the body and the electrodes, resistance of the air over the body surface from one conductive portion to another, resistance through the body in different paths having different breakdown voltages, and external factors in the apparatus itself.

Another advantage in the use of this apparatus with its high voltages is that it is not always necessary for actual Contact to occur between the electrodes and the body. When the conductivity of the body between the electrodes is high enough, the gap between the electrodes and the body will be ionized. This, of course, permits of more latitude in the body size of material being passed through the apparatus, and of more latitude in the design of the apparatus.

It is, therefore, an object of this invention to provide a simple, inexpensive apparatus of novel design for sorting moving bodies of material according to an electrical characteristic associated with each body.

It is another object of the invention to provide an apparatus for sorting bodies of material moving through a sorting zo'neaccording to the ability of the body to initiate an ionizing discharge type of current flow between electrodes through the body or over the surface of the body.

These and other objects and advantages of the invention will appear from the following description taken in conjunction with the accompanying drawings, in which FIGURE 1 is a front view of one embodiment of apparatus according to the invention;

FIGURE 2 is aside view, partly in section, of the apparat'us of FIGURE 1;

FIGURE 3 is a schematic diagram useful in explaining the operation of the apparatus of FIGURES 1 and 2;

FIGURE 4 is a schematic diagram showing another embodiment of the invention;

FIGURE 5 is a partial front view of another'embodimerit of the invention;

FIGURE 6 is a partial side view of the embodiment of FIGURE 5; I

FIGURE 7 is a partial front view of yet another embodiment of the invention;

FIGURE 8 is a partial side view of the embodiment of FIGURE 7; 7

FIGURE 9 is a graph useful in explaining the invention;

FIGURE 10 is a partial side view of a variation of the embodiment of FIGURES 7 and 8, and

FIGURE 11 is a partial front view of the apparatus of FIGURE 10.

It will be apparent that the apparatus of this invention will not function where the insulating properties of the bodies of material are greater than, or are of substantially the same value as, that of the gas or fluid normally present between the electrodes in the absence of such a body of material.

Referring now to FIGURES 1 and 2, an ore sorting apparatus is shown which sorts ore fragments moving through it in a wide path random stream. The expression wide pat as used herein is intended to mean a path of travel having 'suflici'ent width to permit a plurality of the bodies using it to move along the path in side by side relationship. The term random stream as used herein is intended to mean a plurality of objects moving in a given direction and having a haphazard alignment and spacing.

In the following description the wide path random stream extends in a straight line. It is intended, however, that the wide path stream could be uniformly curved, and in fact, where required, could be a uniformly curved path closing on itself to form a circle in crosssection. In other words, in an apparatus having a hopper feeding bodies into a cone shaped path director, the path followed by the bodies down the cone would be considered as a wide path random stream.

In FIGURES 1 and 2, a hopper 10 is shown holding a quantity of ore or rock fragments 11. The ore fragments move downwards under the influence of gravity onto a vibrating table 12 suspended by springs 14. A number of springs 14 are used but only a limited number are shown in FIGURE 2 for simplicity of drawing. A connecting member 15 joins the table 12 to a vibrating motor 16. The vibrating motor 16 may also have a spring suspension. Such vibrating table feeders are well known in the art. The vibration of table 12 tends to distribute the fragments 11 over the surface of the table and at the same time to cause the fragments 11 to move down the sloping table surface in a wide path random stream. The rate of feed onto the table is such that the fragments are all in contact with the table as they move down its surface. A wide path feeder of this type is described, for example, in a copending United States patent application Serial No. 206,095, of James F. Hutter et al., filed June 28, 1962, now Patent No. 3,179,247 and assigned to the same assignee as this application.

As the fragments 11 reach the end of table 12 they drop onto a trajectory plate or guiding plate 17. In: the embodiment of FIGURES 1 and 2 the plate 17 is: preferably made of insulating material as will be dis-- cussed hereinafter. The trajectory plate 17 has a fairly steep slope and the fragments move down its surface under the influence of gravity. Thus the plate 17 defines a predetermined wide path and directs the fragments from its lower end in this path.

Positioned just below the end of trajectory plate 17 are a plurality of high voltage electrodes 20-30 in spaced side by side relationship extending across the width of the path. The electrodes 20-30 each having a terminating end closely spaced from the predetermined path of the fragments as they leave plate 17. The electrodes 20-30 may be mounted by insulating means from plate 17. The electrodes are thus insulated from one another, and if plate 17 is of conducting material they are insulated from it by the mounting and spaced from it. In FIGURE 2, a typical mounting is shown for electrode 30 and comprises a mounting bracket 32 extending from plate 17 to electrode 30.

A plurality of fluid nozzles 33-37 are mounted adjacent the fragment path below electrodes 20-30 and in side by side relationship extending across the width of the path.- The nozzle and electrode arrangement is shown in a preferred form in FIGURES 1 and 3 where electrodes 21, 23,.

25, 27 and 29 are positioned directly above the centers of.

fluid nozzles 33, 34, 35, 36 and 37, respectively. The: other electrodes are positioned above the edges or junc-- tions of the nozzles as shown. The nozzles 33-37 are: spaced a sufiicient distance from electrodes 20-30 to prevent undesirable discharge therebetween, or, of course, nozzles 33-37 could be made of an insulating material. Each of the nozzles 33-37 is connected through a respective control valve 33-43 to a source of fluid under pressure. This fluid is conveniently air under pressure. The valves 39-43 are controlled by a sorting signal to be in one of two conditionsopen or closed. When a valve is open, the blast of air is directed through the associated nozzle at fragments passing the nozzle. The air blast deflects fragments from their normal path of fall. Such an air blast rejection means is described, for example, in United States Patent 3,097,744 issued July 16, 1963 in the name of J. F. Hutter et :11.

It will be apparent that a mechanical rejection means could be used in the invention rather than one employing a fluid blast. Mechanical rejection means where plates are moved to deflect rejected bodies, or where rods push rejected pieces to one side, are relatively slow acting. They are more suitable to sorting systems where the bodies to be sorted are not in free fall. Such mechanical rejection means could be used with the present invention where the rate of sorting is not high. Thus, the phrase rejection means as used herein refers to any means forshifting or deflecting a body of material from a normal path through the sorting zone in response to the presence or absence of a signal from the detection means. When bodies of material are being sorted in free fall, the use of an air blast rejection means is preferred.

A splitter plate 13 is mounted below the rejection means to separate or divide the fragments after they pass the rejection means. The fragments which are not deflected follow one path and fall on one side of plate 13 onto a belt 18 to be carried to one destination. The fragments which are deflected follow another path and fall on the other side of plate 13 onto a belt 19 to be carried to another destination.

Referring now to FIGURE 3, the circuit of the apparatus is indicated schematically. The electrodes 20, 22, 24, 26, 28 and 30 are connected together by a conductor 44 which may be grounded. Adjacent electrodes may thus be considered as a pair of cooperating electrodes, and one electrode in each pair is connected to the conductor 44 or grounded. Thus, electrodes 20 and 21 form one pair, electrodes 21 and 22 form another pair, electrodes 22 and 23 another, and so on. A high voltage source of alternating current 45-54 is connected between each pair of electrodes so that a high voltage source 45 is between electrodes 20 and 21, high voltage source 46 is between electrodes 21 and 22, and so on. With an electrode spacing of about /4 inch, a high voltage supply providing pulses of 10,000 volts at a frequency of several kilocycles has been found to be satisfactory. The voltages may, of course, be varied. The required voltage is dependent on the type of ore to be sorted and on the quality of the ore. For each high voltage source 45-54 there is a current flow detector 56-65 connected to its respective source. The detector may be conveniently connected to the primary or secondary Winding of the pulse transformer in the power supply. Whenever there is an ionizing discharge between a pair of electrodes, the associated current flow detector provides an output signal. A discriminator may be included in the detector so that the ionizing current iiow must exceed a predetermined level before the output signal is provided. Circuits and devices which are responsive to current flow to provide an output signal are well known and further description is believed to be unnecessary. The outputs of detectors 56-65 are connected to timing stages 67-71 so that an output signal from either of detectors 56 or 57 will operate timing stage 67, and an output from either of detectors 58 or 59 will operate timing stage 58 and so on. The timing stages 67-71 in turn provide a control signal to the respective one of control valves 39-43 to actuate the valve as a fragment passes in front of the respective one of rejection nozzles 33-37. The purpose of the timing stage is to ensure that the air blast from the nozzle occurs as the fragment triggering the air blast is in front of the nozzle. An example of such a timing stage may be found in the aforementioned United States Patent 3,097,744. In some instances the delay in the control valve will be sufiicient to provide the required synchronization and a separate timing stage would not be required.

The timing stage may include means to vary the length of the individual air blast. That is, an individual triggering signal from the detection means may be of a very short duration and it may be desirable under different circumstances to have this triggering signal result in an air blast of a short duration or result in a longer air blast. For example, when using a high voltage supply that is pulsed at a high frequency, a particular body of material may be electrically stressed (subjected to individual high voltage pulses) many times as it passes the high voltage electrodes. The number of high voltage pulses to which a body is subjected depends on the length of the body, the speed of the body past the electrodes, and the frequency of the high voltage pulses. Any or all of these pulses may produce an ionizing current flow of sufficient magnitude to cause a triggering signal from the detection means capable of resulting in an air blast. It will be seen that if a body of material has the necessary electrical characteristics to cause ionizing current flow, the number of triggering signals will be related to the size of the body of material. If the duration of each air blast pulse is short, the resulting number of air blast pulses or the total air blast will also be related to the size of the body of material. In other words, if a large and a small body of material having the same electrical characteristics per unit mass are passed through the sorting apparatus as described, the large body would result in a greater total air blast than the small body. Thus, the deflecting force applied to the large body by the air blast would be greater than the deflecting force applied to the small body, other things being equal. This is, of course, very desirable, particularly when there is a considerable difference between the sizes of the large and small bodies of material. It is desirable not only because it conserves air by relating the air blast to the size of the body of material, but also because it permits the ap paratus to sort to grade.

The final result of whether or not a piece or body of material is deflected will depend on the number of high voltage pulses which result in ionizing current flow and consequently on the number of short duration air blast pulses directed at a body in proportion to its mass. If the number of air blast pulses (i.e., the total air blast per body) is insufficient to deflect the body mass, then the body of material will follow the normal path through the apparatus. This factor is of considerable importance in making the apparatus sort to grade, that is in making the apparatus sort to a particular desired quality. The greater the concentration of material per unit mass causing an ionizing discharge, the greater will be the total air blast per unit mass within the limits of the apparatus.

The length of the individual air blasts may be varied from a minimum necessary for operation of the air blast valve (which may be as low as the order of four milliseconds) to a length sufiicient to cover the passage of the largest body of material. The variation in the length of the air blast pulses will affect the operation of the apparatus in sorting to grade and may be used to some degree to control the quality of the ore being sorted. Also, as was previously mentioned, the grade or quality of the sorted ore may be controlled by varying the high voltage or by varying the level of ionizing current flow which will result in an air blast.

It will, of course, be apparent that when using a high voltage DC. supply, the control of the quality of the ore would depend on adjustment of the high voltage, level or on the discriminating level used to discriminate between various levels of ionizing cur-rent flow.

Returning now to the embodiment of FIGURES 1, 2 and 3, the operation of this embodiment will be apparent.

The fragments 11 slide down the trajectory plate 17 and fall off the end. The fragments pass immediately by the electrodes 2030. Each fragment substantially bridges at least a pair of electrodes, and each fragment in its pas sage is stressed electrically. Rocks may be classed generally as non-uniform dielectrics which, in many cases, may have highly conductive inclusions (e.g. metal sulphides), and may have contiguous or discrete pores containing liquids or gases. Provided that there is a sufiicient proportion of a conductive fraction or inclusion present in a fragment, an ionizing discharge is produced. If there is sufficient current flow produced, the flow is detected by one of detectors 56-65 and the respective one of timing stages 67-7-1 actuates a respective one of control valves 39-43 to direct a blast of air at the fragment and alter its path of fall.

It is desirable to place the electrodes 20-30 fairly close to plate 17 because the path of the fragments is more closely defined towards the end of the plate. However, there must be no arcing or current flow between electrodes and plate 17 as the fragments fall. As was previously mentioned, to avoid such undesirable current flow, the plate 17 may be made of insulating material. Alternatively, the electrodes may be spaced from the plate far enough to avoid this. Similarly, the nozzles 33-37 should be either of insulating material or spaced far enough from electrodes 20-30 to avoid undesirable current flow.

It should be noted that generally it is preferable that the fragments be surface dry. It has been found that the surface water path may have a resistance somewhere in the range of about 100K ohms to 500K ohms. This surface resistance may be negligible in an ore such as a metal sulphide which may have a resistance in the range of about 1 to 100 ohms. However, for other types or ore with a higher resistance, the surface water resistance may become significant and the apparatus will not function satisfactorily.

It will be apparent that the invention could be applied to sorting bodies of material moving in single row alignment. Only one pair of electrodes would be required, and, of course, only one of each of the associated components such as power source, detector, timer and fluid nozzle.

It will be also apparent that with the apparatus shown in FIGURES 1-3 which has five fluid nozzles in the rejection means, an arrangement having six electrodes instead of eleven electrodes could be used. That is, the appara'tus could be arranged for operation with electrodes 20, 22, 24, 26, 28 and 30, the other electrodes being omitted. Then electrodes 20 and 22 would form one pair, electrodes 22 and 24 another, and so on. Thus, there would be five pairs of electrodes, five high voltage sources and five detectors which would be connected to the five timing stages. With such an arrangement, fewer electrodes, supplies and detectors would be required, but the coverage across the path would not be as complete. For the same path width and with the same number of nozzles, smaller fragment sizes may be sorted with the preferred arrangement shown in the drawings.

Referring now to FIGURE 4, there is shown a schematic drawing of another embodiment where only five elec.

trodes are used. The electrodes are in the form of plates which present a flat terminating discharge surface towards the fragment path. These electrodes are designated 73- 77, and each electrode extends across the width of the wide path approximately the same distance as the fluid nozzle directly below it. The trajectory plate '17, in this embodiment is made of conducting material, or at least its lower edge is of conducting material, and serves as a common electrode forming, in effect, a pair with each of the electrodes 73-77. The eifective pair of electrodes are in juxtaposition with the fragment path, the common electrode being adjacent the path and the other electrode closely spaced from the path. High voltage sources 78-82 are connected across each pair of electrodes source 78 being connected between electrode 73 and common electrode 17, source 79 being connected between eletrode 74 and common electrode 17, and so on. Current (flow detectors 84-88 are connected respectively to high voltage sources 78-82 and these detectors provide a signal to initiate operation of timing stages 67-71. The timing stages 67-71 are the same as those described in connection with FIGURES 1-3, as are the control valves and rejection means.

The operation of the FIGURE 4 embodiment is similar to that of the embodiment of FIGURES 1-3. Fragments 11 slide down the trajectory plate 17, and as they move off the end they substantially bridge the space between the plate 17 which serves as the common electrode and one of the electrodes 73-77. If the electrical characteristics of a fragment are such that they cause ionizing discharge current flow, this is detected by the respective one of detectors 84-88 and an air blast is initiated when the fragment passes the respective nozzle as before.

When an ionizing discharge current flow is initiated the voltage at the respective plate electrode 73-77 will drop almost to the voltage on the common electrode 17. Consequently, there must be sufiicient spacing between adjacent electrodes in electrodes 73-77 to prevent ionizing discharge between them when the voltage on one drops.

The FIGURE 4 embodiment does not have quite as long an open path distance included in the path from one electrode of a pair electrode through a fragment to the other electrode because of the fragment is actually in contact with the common electrode or trajectory plate.

Referring now to FIGURES 5 and 6, an embodiment is shown in which the air path distance or open path distance between electrodes and the fragment surface is reduced. As in the FIGURE 4 embodiment, the trajectory plate 17, or at least its lower edge, is of a conducting material and constitutes a common electrode. However, the plate electrodes of FIGURE 4 are replaced by spring electrodes 91-95. Electrodes 91-95 may be arranged in adjacent groups having at least one electrode in a group. In other words, each spring electrode by itself may be considered as a group and each group form with the common electrode 17 a cooperating pair. A high voltage power supply would then be connected between each spring electrode and the common electrode 17. Alternately, two adjacent spring electrodes might be electrically connected together and considered as a group and each group would form with the common electrode a cooperating pair of electrodes. In this latter case, one power supply, one detection means and one rejection means would be associated with the group of two as indicated in FIGURE 5. A group of electrodes could also have more than two electrodes in its, but the numher would be limited by practical physical considerations such as the coverage necessary, the size of the spring electrodes, the size of the rejection nozzle, the spacing necessary, etc. It has been found that for many applications, two electrodes in a group, as shown, provide satisfactory coverage and operates adequately.

Electrodes 91-95 may be mounted to brackets 96-100 which are in turn mounted by insulating means to plate 17. Preferably, brackets 96-100 are of insulating material. However, other materials may be used as long as electrodes 91-95 are insulated from plate 17.

As before, electrodes 91-95 must be spaced from plate 17 a sufiicient distance to prevent open pathway ionizing discharge therebctween. There must also be suflicient distance between electrodes 91-95 and the rejection nozzles (only nozzles 33 and 34 are shown in FIG- URE 5). Also, the spacing between electrodes in the group of electrodes 91-95 which might have a potential difference should be spaced to prevent unwanted ionizing discharge. That is, for example, if a rock fragment initiates an ionizing discharge between electrode 92 and common electrode 17, the voltage on electrode 92 will fall. This would cause a voltage difference between electrodes 93 and 92 but the spacing should inhibit discharge between electrodes 93 and 92.

The spring electrodes 91-95 have terminating ends which project very slightly into the path of falling fragments. There is, therefore, normally a contact with some portion of a fragment falling past the electrode. Depending on the rock fragments presentation and its surface configuration, the contact may be momentary,

it may be at spaced points on the surface, or it may be continuous over a portion of the surface. At any rate, the air path distance is normally reduced to a minimum at some point in the passage of the fragment. As before, the fragment may or may not cause an ionizing discharge type current fiow depending on the high voltage setting and the rock characteristics.

The spring electrodes 91-95 are of a construction and arrangement such that they are damped. In other words, once a rock fragment engages a spring and displaces it, the spring should quickly return to its rest position once the fragment passes. It has been found that a helical extension spring made with pretension may provide sufficient damping. Such helical springs of the order of & diameter and 3" in length have been found satisfactory in one installation.

It is believed that the operation of the embodiment of FIGURES 5 and 6 is apparent. Fragments pass down trajectory plate 17 and move off the end in a Wide path random stream. Each fragment bridges or substantially bridges a gap between plate 17 and one of electrodes 9195. For example, a fragment may bridge between 17 and electrode 91. A high voltage power supply 78 is connected to apply a high voltage across electrodes 17 and 91, and the fragment may be of a composition to initiate an ionizing discharge. As in FIGURE 4, the discharge current flow is detected and a signal developed to actuate a control and direct an air blast from nozzle 33 deflecting the fragment.

The apparatus of this invention has been used to sort rocks of the base metal type. The metal sulphides which represent the desired constituent have been found to impart a low effective high voltage resistance of perhaps one to 100 ohms to a fragment of high quality ore. The waste associated with the various ores may, on the other hand, have a very much higher resistance, perhaps, for example, in excess of a megohm. There is a considerable separation in the two effective high voltage resistances and no problems are encountered in establishing a working cut-off point between ore and Waste fragments, so that a predetermined concentration of the desired constituent will effect a discrimination. While the irregularities of rock presentation and discontinuities of metal sulfide content may appear to introduce undesirable variables, these variables are not sufficient to prohibit sorting where a difference of the resistances of ore and waste are of the magnitudes generally encountered in practice.

Referring now to FIGURES 7 and 8, there is shown an embodiment of the invention that is quite similar to that of FIGURES 5 and 6. In FIGURES 7 and 8, a series of spring electrodes, of which 101, 102, 103 and 104 are shown, are mounted to an insulating mounting bar 106. The bar 106 is above trajectory plate 17 and the electrodes are directed towards plate 17. Preferably the spring electrodes 101-104 are inclined in the direction of movement of ore fragments down to the surface of plate 17 as seen in FIGURE 8.

The spring electrodes 101-104 may be helical springs as before and may have a projecting terminating end spaced from plate 17. The electrodes are preferably critically damped to prevent vibration or oscillation.

At the lower end of trajectory plate 17 there are a series of fluid nozzles in side by side relationship extending across the path of the fragments. Nozzles 33, 34 and part of 35 can be seen in FIGURE 7. The position of the spring electrodes in this embodiment permits the nozzles to be positioned closely adjacent the lower end of the trajectory plate 17 where the action of the blast from the nozzles has been found to be quite effective.

The spring electrodes 101104 may be arranged in adjacent groups having at least one spring electrode in each group. The connections would be similar to those described in connection with FIGURES 5 and 6. In the preferred form shown in FIGURE 7 there are two electrodes in a group. Thus, the electrodes 101 and 102 comprise one group and 'with the common electrode trajectory plate 17 form a cooperating pair of electrodes. A high voltage power supply 78 has one terminal connected to electrodes 101 and 102 and the other terminal connected to common electrode 17. The remaining spring electrodes would be similarly connected as described in connection with previous embodiments.

The operation of the FIGURES 7 and 8 embodiment is similar to that of FIGURES 5 and 6. Each fragment as it passes down plate 17 bridges the space between at least one of the spring electrodes and plate 17. That is, each fragment as it moves down plate 17 engages at least one spring electrode or passes very close to the tip of at least one spring electrode. The fragment may initiate an ionizing discharge current flow of some degree. If the current is sufficient a signal actuates a respective nozzle or nozzles to direct an air blast at the fragment initiating the ionizing discharge to deflect it from its path.

Referring now to FIGURE 9, there is shown a graph of current (in milliamperes) slotted against electrode voltage (in kilovolts). The values indicated in the graph were obtained using a particular sample of banded specular iron ore placed between electrodes of apparatus according to this invention, and by varying the amplitude of high voltage pulses while observing current flow. The values indicated may include factors external to the rock sample under test. The graph is included only as an example of a voltage-current relationship (i.e. of effective resistance) extended to higher voltage ranges and showing the occurrence of an ionizing type of discharge.

At low values of applied electrode voltage, allowing for stray capacitance, the current is proportional to the voltage following Ohms Law. This may be referred to as the linear portion of the graph, indicated as 110, and extending from zero to a breakdown point 111. The voltage at which breakdown occurs and ionizing discharge begins is not a precise voltage, but is rather a narrow voltage range. Because of the scale used in the graph, the linear portion of the curve is shown with little slope lying close to the voltage axis. As the voltage is increased past the first breakdown point 111, the ionizing type current flow increases as is indicated by portion 112 of the curve on the graph. The relationship shown by portion 112 is not linear, and for the same overall voltage change there is a greater current change in portion 112 than in linear portion 110. Thus, it is more desirable to use the region indicated by portion 112 to discriminate between different current flow values for different specimens. This is so because (1) there is a larger current flow for any given voltage in the portion 112, and the measurement of larger currents normally involves more rugged equipment, and (2) there is a greater current change for a given voltage change permitting less critical discrimination in portion 112.

As the voltage is increased, a second breakdown point 114 is reached for this ore sample. A further increase in electrode voltage results in a current increase as shown by portion 115 until the region 116 is reached. The useful portion of the grap for the purposes of this invention extends only to region 116.

The following table is also included to indicate the breakdown voltages and effective resistances in the linear region (below the breakdown voltage) and in the nonlinear region (above the breakdown voltage), for some different ore samples. It should be noted that the readings, as before, may include various factors external of the rock sample, and that the measurements are taken using on the electrodes a high voltage pulse rather than a constant unidirectional voltage. As a result, the calculated effective resistance in the low voltage or linear region is not truly linear as it should be in accordance with Ohms Law. However, the variation from linear in the low voltage region is not of great significance, and in FIGURE 9, such variation is not apparent.

As was previously mentionedthe breakdown voltages are not precise voltages but are rather a narrow voltage range, characterized by random pulses or-abnormally high current.

In the preceding description the high voltage electrode supply has been referred to as supplying a high pulsed voltage. The voltage of the supply may be varied in value to suit difierent circumstances and 'for different ores. It will be apparent that other variations may be beneficial in some instances. For example, a DC. high voltage supply may be used or the frequency ofthe pulsed supply might be varied from a very low level 'to well into the higher frequency region. Also, it might be desirable to use different waveforms for the pulses under various circumstances. Other alternatives will be apparent to those skilled in'the art.

The apparatus of this invention could be arranged to blast or deflect bodies of material which did not initiate an ionizing discharge current fiow or which did not provide a high enough ionizing discharge current flow.

Thus, in the invention, the rejection means may be responsive to the presence or absence of a signal from the detection means. As another alternative, the voltage may be raised until there is a-continuous ionizing type of discharge between the electrodes, and the air blast inhibited until the discharge is interrupted. Bodies of material having dielectric properties suflicient to interrupt the discharge would then be deflected. If desired, as one variation, a beam of light and opposed photocell could be arranged to start the steady discharge just before the approachof a body thereby reducing duration-of the steady discharge. As another variation, the beam of light and the opposed photocell could be arranged so that theinterruption of the beam of light by an intruding body of material would initiate a fluid blast unless the blast was inhibited by a signal from the detection means. The signal from the detection means could be responsive to an ionizing current flow of a predetermined magnitude as previously described. Apparatus suitable for thisis indicated in FIGURES and 11.

Referring brieflyto FIGURES 1'0 and .11, there is shown apparatus quite similar to that of FIGURES 7 and 8. As before, a series of spring electrodes-101-104 are mounted to an insulating bar 106 above trajectory plate '17. However, in FIGURES .10 and .11, the fluid nozzles 33-35 are spacer from the lower end of trajectory plate 17 and a light source 120 with opposed photocells are positioned on opposite sides of the fragment path just below the end of plate 17. The light source 120 extends across the entire Width of the .sorting zone and projects a beam of light across the path of the'falling fragments. A series of photocells 121-123 are positioned to receive light from the light source 120. There is preferably one photocell for each fluid nozzle, and each photocell is aligned with its respective nozzle as can be seen in FIGURE 11. The photocells 121-123 may have openings that are narrow in the direction of movement of the fragments, and the source may provide :a .correspondingly narrow beam. That is, the beam of light between the source and the photocells will cover the entire area through which fragments may fall, but it will be of limited thickness to provide a more accurate determination of the time at which the leading and trailing edge of a fragment pass the photocells.

Each photocell is connected to the control for fluid flow of the respective nozzle and initiates a fluid blast at each fragment pasing the nozzle unless it is inhibited by a signal from the detection means derived from the same fragment. In this apparatus, it is preferable that the fluid blast be a relatively long one lasting for the duration of the passage of the fragment.

It will, of course, be apparent that the light source and photocell arrangement may be used with the other embodiment described herein if the circumstances require it.

The embodiments of the apparatus described refer to the rockfragments or other bodies moving in an air medium between the electrodes. It might be desirable, for example to increase the voltage at which an ionizing discharge occurs, to move the bodies past the electrodes in a liquid medium such as an oil medium, or to use as a medium a gas other than air to blanket the inter-electrode region.

It is believed that the embodiments of the invention described herein are typical. The invention provides a simple, inexpensive and rugged apparatus for sorting bodies of.material having differing electrical characteristics. Various modifications and variations can be made to the'embodimentsdescribed without departing from the true invention as defined inthe appended claims.

We claim:

1. Apparatus for sorting bodies of material moving through a sorting zone, comprising handling means for introducing bodies of material into .the upper part of said sorting zone for movement therethroughunder the influence of gravity in a predetermined path,

at least-a pair of high voltage electrodes mounted in said sorting zone having terminating discharge ends in juxtaposition with said path and having a spacing between said ends preventing .open pathway current flow,

current flow detection means connected to said electrodesresponsiveto a predetermined level of ionizing discharge current flow for developing a signal with movement of a body ofmaterial along said path past said electrodes,

rejectionmeans positioned in said sorting zone below said electrodes having a first condition where bodies are moved to a first path and a second condition Where bodies are moved to a second path,

said rejection means normally being in said first condition, and

means responsive .to said signal from said detection means controlling said rejection means.

2. Apparatus for sorting bodies of material the constituents of which have different electrical characteristics as the bodies move through a sorting zone, comprising handling means for introducing bodies of material in single row alignment into the upper part of said sorting zone for movement therethrough under the in- ;fluence of gravity along apredetermined path,

.a pair of high voltage electrodes mounted in the sorting zone having terminating discharge ends in juxtaposition with said path and having a spacing between said ends preventing open pathway current flow,

current flow detection means connected to said electrodes responsive to an ionizing discharge current flow for developing a signal with movement of a discharge initiating body of material along said path past said electrodes,

a fiuidnozzle having a control for fluid flow therethrough positioned adjacent saidpath and below'said stituents of which have diflerent electrical characteristics the bodies move through a sorting zone, comprising a wide path feeder delivering a Wide path random stream of bodies of material to said sorting zone for movement therethrough along a predetermined path,

a plurality of high voltage electrodes mounted in side by side relationship extending across the width of said path and having terminating ends in juxtaposition with said path,

said electrodes having a spacing between adjacent ones thereof suflicient to prevent open pathway current flow therebetween,

adjacent ones of said electrodes forming cooperating pairs,

adjacent pairs of electrodes defining adjacent portions of said path along which said bodies move,

a current flow detection means for each said pair connected to the eelctrodes in the respective pair,

each said detection means being responsive to a predetermined level of ionizing discharge current flow for developing a signal with movement of a body of material along the portion of the path past the respective pair,

a plurality of fluid nozzles each having a control for fluid flow therethrough positioned adjacent said path in side by side relationship so that said bodies pass the nozzles after passing the electrodes,

said nozzles extending across the width of the path with each nozzle extending a distance equal to an integral number of said adjacent portions of said path, and

means for each said nozzle responsive to said signal from said detection means associated with a portion of said path across which a respective nozzle extends controlling fluid flow through the nozzle.

4. Apparatus for sorting bodies of material the constituents of which have different electrical characteristics the bodies move through a sorting zone, comprising a wide path feederdelivering a wide path random stream of bodies of material to said sorting zone for movement therethrough along a predetermined path,

a plurality of high voltage electrodes mounted in side by side relationship extending across the width of said path and having terminating ends in juxtaposition with said path,

said electrodes having a spacing between adjacent ones thereof sufficient to prevent open pathway current flow therebetween,

adjacent ones of said electrodes forming pairs,

adjacent pairs of electrodes defining adjacent portions of said path along which said bodies move,

a current flow detection means for each said pair connected to the electrodes in the respective pair,

each said detection means being responsive to an ionizing discharge current flow for developing a signal with movement of a discharge-initiating body of material along the portion of said path past the respective pair,

a plurality of fluid nozzles each having a control for fluid flow therethrough positioned adjacent said path in side by side relationship so that bodies pass the nozzles after passing the electrodes,

said nozzles extending across the width of the path with each nozzle extending a distance equal to an integral number of said adjacent portions of said path, and

cooperating means for each said nozzle responsive to a signal from a detection means associated with a portion of said path across which a respective nozzle extends actuating the respective control for fluid flow and initiating fluid flow through the nozzle to deflect a body from its path.

5. Apparatus as defined in claim 4 in which each nozzle extends across one of the adjacent portions of said path.

6. Apparatus as defined in claim 4 in which each nozzle extends across two of the adjacent portions of said path.

7. Apparatus for sorting ore fragments moving through a sorting zone, comprising a wide path feeder for delivering a wide path random stream of fragments to the upper part of said sorting zone,

a trajectory plate mounted in the sorting zone below said feeder for receiving said stream and being inclined to guide said fragments down its surface under the influence of gravity,

said trajectory plate defining a predetermined wide path for said stream of fragments,

a plurality of high voltage pulsating current electrodes mounted in side by side relationship below said trajectory plate and extending across the width of the path,

said high voltage electrodes having terminating discharge ends closely spaced from said path and having a spacing between adjacent electrodes of a size suflicient to prevent open pathway current flow therebetween, adjacent ones of said electrodes forming a cooperating pair,

a current flow detection means for each said pair connected to the electrodes in the respective pair,

each said detection means being responsive to an ionizing discharge current flow for developing a signal with movement of a discharge-initiating fragment along said path past the respective pair,

a fluid nozzle for each two adjacent pairs of electrodes each having a control for fluid flow therethrough and each nozzle being positioned so that fragments pass it after passing either of the two respective adjacent pairs of electrodes,

said nozzles being in side by side relationship and extending across the width of said path, and

means for each said nozzle responsive to signals from two detection means connected to the two respective pairs actuating the respective control for fluid flow and initiating fluid flow through the nozzle to deflect a fragment from its path.

8. Apparatus for sorting ore fragments moving through a sorting zone, comprising a Wide path feeder for delivering a wide path random stream of fragments to the upper part of said sorting zone,

trajectory plate mounted in the sorting zone below said feeder for receiving said stream and being inclined to guide the fragments down its surface under the influence of gravity,

said trajectory plate defining a predetermined wide path for said stream of fragments,

said trajectory plate having at least a lower end of conducting material,

a plurality of high voltage plate-like electrodes mounted in side by said relationship below said trajectory plate and extending across the width of the path,

said high voltage electrodes having flat terminating discharge ends closely spaced from said path and having a spacing from the end of said trajectory plate of a length preventing an open pathway discharge thereto,

each said high voltage electrode forming with the end of said trajectory plate a cooperating pair of electrodes,

a current flow detection means for each said electrode connected to a respective electrode and to the trajectory plate,

each said detection means being responsive to an ionizing discharge current flow for developing a signal with movement of a discharge-initiating fragment along said path past the respective electrode,

a fluid nozzle for each said electrode each having a control for fluid flow therethrough,

said nozzles being mounted in side by side relationship below said electrodes and adjacent said path,

each said nozzle extending across substantially the same portion of said path asia respective electrode, and

means for each said electrode responsive to 'a "signal from a detection means :connected to a respective electrode actuating the respective control fortfluid flow and initiating fluid flow through the respective nozzle to deflect a fragment from its path.

9. Apparatus for sorting ore fragments movingthrough a sorting zone, 1 comprising a wide path feeder for delivering'a wide-pathrandom stream of fragments to the upper'part of said sorting zone,

a trajectory plate mounted in said sorting :zone below said feeder for receiving said stream and being inclined to guide the fragments down'itssurface under the influence of gravity in a 'wide path random stream,

said trajectory plate having at least a lower discharge end of conducting material,

a plurality of helical spring high voltage electrodes mounted in side by side relationship 'belowtsaid trajectory plate extending across'the width of said path and having a spacing therebetween preventing current flow,

said spring electrodes having ends terminating just within said path and'being spaced from 'the end of said trajectory plate adistance sufficientto prevent open pathway current fiowjtherebetween,

said spring electrodes being arranged in adjacent groups having at least one electrode in a group :and each said group forming with the end of the trajectory plate a pair of cooperating electrodes,

a current flow detection means for each said pair responsive to an ionizing discharge current flow for developing a signal with movement of a dischargeinitiating fragment along said path'past the respece tive pair,

a fluid nozzle for each said detection meanseach having a control for fluid flow therethrough and each nozzle being positioned so that fragments pass it after'passing said spring electrodes,

said nozzles being in side by side relationship extending across the width of said path, and

means for each said nozzle responsive to signals from the respective detection means for actuating the respective control for fluid flow and initiating fluid flow through the nozzle to deflect the discharge-initiating fragment from its path.

10. Apparatus as defined in claim 9 in which'the spring electrodes are highly damped to reduce vibratory motion and in which two adjacent electrodes are connected to form with the end of the trajectory-plate a common pair.

11. Apparatus for sorting'ore fragments moving through a sorting zone, comprising a wide path feeder for delivering a wide path random stream of fragments to the upper part of said sorting zone,

a trajectory plate mounted in said sorting zone below said feeder for receiving said stream and being inclined to guide the fragments down its surface under the influence of gravity in a wide path random stream,

said trajectory plate having at least a lower discharge end of conducting material,

a plurality of helical spring high voltage electrodes having a mounting end and a terminating end mounted at said mounting end in spaced side by-side relationship opposite a conducting portion of said trajectory 'plate extending-across the width of said path,

said spring electrodes extending from said mounting end in a direction towards said trajectory plate and having terminating ends spaced from said trajectory plate a distance sufficient to prevent open pathway current flow therebetween,

said spring electrodes being arranged in adjacent groups having at least one electrode-in a .group and each groupforming with the conducting portion of said trajectoryplate a pair of cooperating electrodes,

a current flow detection means for'each said pair re- :sponsive to an ionizing discharge-current flow for developing a signal with movement of a fragment along said path past the respective pair,

afluid' nozzle for'each said detection means eachhaving a control for fluid flow therethrough and each nozzle being positioned so that fragments pass it after passing said spring'electrodes,

said nozzles being in side by side relationship extending across the width of said path, and

means for each saidnozzle responsive to signals from the respective detection means for actuating the respective control for fluid flow and initiating fluid flowthrough the nozzle to deflect the discharge-initiating fragment from its path.

-12. Apparatus as defined in claim 11 in which the spring electrodes are damped to reduce vibrating motion and in which the spring electrodes are inclined towards their terminating ends in the direction inwhich thepath extends.

-13. Apparatus for sorting ore fragments moving through a sorting zone comprising,

a wide path feeder for delivering a wide path random stream of fragments to the upper part of said sorting zone,

a trajector plate mounted in said sorting zone below said feeder for receiving said stream and being inclined to guide the fragments down its surface under the'influence of gravity in a wide path random stream,

said trajectory plate having at least a lower discharge end of conducting material,

aplurality of helical spring high voltage electrodes each :having a mounting end and a terminating discharge end,

.said spring electrodes being mounted at said mounting end in spaced side by side relationship opposite a conducting portion of said trajectory plate and extending across the width of said path,

said spring electrodes extending from said mounting end to said terminating end in a direction towards said conducting portion and said terminating ends being spaced from said conducting portion by a distance to just maintain'an open pathway ionizing discharge current'flow,

said spring electrodes being arranged in adjacent groups having at least one electrode in a group and each group forming with said conducting portion of said trajectory plate a pair of cooperating electrodes,

a current flow detection means for each said pair of electrodes responsive to interruption of ionizing discharge current flow by'movement past the respective pair of electrodes of a fragment having higher dielectric properties than the medium otherwise between said electrodes to develop a signal,

a fluid nozzle for each said detection means each having a control for fluid flow therethrough and each nozzle .being positioned so that fragments pass it after passing said spring electrodes,

said nozzles being in side by side relationship extending across the width of said path, and

means for each said nozzle responsive to signals from the respective detection means for actuating the respectivecontrol for fluid flow and initiating fluid flow through the nozzle to deflect the discharge-interrupting body from its path.

14. Apparatus for sorting bodies of material which have diiierent electrical characteristics as the bodies move through a sorting zone comprising,

means defining a predetermined path through said sorting zone for said bodies of material,

means for directing bodies of material along said path,

at least a pair of high voltage electrodes mounted in said sorting zone and having terminating ends in juxtaposition with said path,

ionizing current flow detection means connected to said electrodes and responsive to changes in current flow with movement of a body of material past the electrodes to develop a first signal,

rejection means positioned in said sorting zone so that said bodies of material pass it after passing said electrodes,

a light source on one side of said path for directing a beam of light across said path,

a photocell on the side of said path opposite said light source for receiving light therefrom and being responsive to occultation of said light beam by a body of material to develop a second signal,

said light source and photocell being positioned so that bodies of material pass between them before passing said rejection means, and

means responsive to said second signal to operate said rejection means in the absence of said first signal.

15. Apparatus for sorting irregularly shaped bodies of material moving through a sorting zone comprising,

means defining a predetermined path through said sorting zone for said bodies of material,

means for directing bodies of material along said path,

at least a pair of high voltage pulsating current electrodes mounted in said sorting zone and having terminating discharge ends in juxtaposition with said pat-h,

a high voltage source providing short duration high voltage pulses connected to each pair of electrodes for applying a pulsating voltage thereto insufficient to sustain an open pathway discharge between the terminating ends of said pair of electrodes,

ionizing current flow detection means connected to said electrodes and responsive to each ionizing current pulse of a predetermined level to develop a signal,

fluid nozzle rejection means positioned in said sorting zone so that bodies pass it after passing said detection means,

said fluid nozzle rejection means including a control for fluid flow therethrough,

means responsive to each said signal from said detection means to actuate said control for fluid flow to direct a short duration fluid blast from said nozzle to impinge upon the body which originated the signal.

16. Apparatus for sorting ore fragments moving through a sorting zone comprising,

a wide path feeder for delivering a wide path random stream of fragments to the upper part of said sorting zone,

a trajectory plate mounted in said sorting zone below said feeder for receiving said stream and being inclined to guide the fragments down its surface under the influence of gravity in a wide path random stream, said trajectory plate having at least a lower discharge end of conducting material,

a plurality of helical spring high voltage electrodes having a mounting end and a terminating end mounted at said mounting end in spaced side by side relationship opposite a conducting portion of said trajectory plate extending across the width of said path,

said spring electrodes extending from said mounting end in a direction towards said trajectory plate and having terminating ends spaced from said trajectory plate a distance s-ufiicient to prevent open pathway current flow therebetween,

said spring electrodes being arranged in adjacent groups having at least one electrode in a group and each group forming with the conducting portion of said trajectory plate a pair of cooperating electrodes,

a high voltage source of pulsating current connected to each cooperating pair of electrodes for applying a pulsating voltage thereto insuflicient to sustain an open pathway discharge therebetween,

current flow detection means connected to each said high voltage source responsive to a predetermined level of a pulse of ionizing discharge current flow between the respective pair of electrodes for developing a triggering signal,

a fluid nozzle for each said detection means having a control for fluid flow therethrough and each nozzle being positioned so that fragments pass it after passing said spring electrodes,

said nozzles being in abutting side by side relationship providing a substantially continuous rejection means extending across the width of said path, and

means responsive to substantially each triggering signal from said detection means for actuating the respective control for fluid flow to initiate a short duration fluid blast through the nozzle to impinge on the discharge initiating fragment.

References Cited by the Examiner UNITED STATES PATENTS 2,504,731 4/50 Rose 20981 3,075,641 1/63 H-utter 209l11.7 X 3,082,871 3/ 63 Duncan 2098-1 3,097,744 7/ 63 Hutter 250223 3,169,626 2/65 Takaesi Miyagawa 209-81 X M. HENSON WOOD, 111., Primary Examiner.

ROBERT -B. REEVES, Examiner. 

1. APPARATUS FOR SORTING BODIES OF MATERIAL MOVING THROUGH A SORTING ZONE, COMPRISING HANDLING MEANS FOR INTRODUCING BODIES OF MATERIAL INTO THE UPPER PART OF SAID SORTING ZONE FOR MOVEMENT THERETHROUGH UNDER THE INFLUENCE OF GRAVITY IN A PREDETERMINED PATH, AT LEAST A PAIR OF HIGH VOLTAGE ELECTRODES MOUNTED IN SAID SORTING ZONE HAVING TERMINATING DISCHARGE ENDS IN JUXTAPOSITION WITH SAID PATH AND HAVING A SPACING BETWEEN SAID ENDS PREVENTING OPEN PATHWAY CURRENT FLOW, CURRENT FLOW DETECTION MEANS CONNECTED TO SAID ELECTRODES RESPONSIVE TO A PREDETERMINED LEVEL OF IONIZING DISCHARGE CURRENT FLOW FOR DEVELOPING A SIGNAL WITH MOVEMENT OF A BODY OF MATERIAL ALONG SAID PATH PAST SAID ELECTRODES, REJECTION MEANS POSITIONED IN SAID SORTING ZONE BELOW SAID ELECTRODES HAVING A FIRST CONDITION WHERE BODIES ARE MOVED TO A FIRST PATH AND A SECOND CONDITION WHERE BODIES ARE MOVED TO A SECOND PATH, SAID REJECTION MEANS NORMALLY BEING IN SAID FIRST CONDITION, AND MEANS RESPONSIVE TO SAID SIGNAL FROM SAID DETECTION MEANS CONTROLLING SAID REJECTION MEANS. 